Scatter type pneumatic sifter



R. RUEGG SCATTER TYPE PNEUMATIC SIFTER Filed Aug. 8. 1966 W 3 .l 3 HP h 2 .h, 1

United States 3,395,796 SCATTER TYPE PNEUMATIC SIFTER Rudolf Ruegg, Zurich, Switzerland, assignor to Escher Wyss Aktiengesellschaft, Zurich, Switzerland, a corporation of Switzerland Filed Aug. 8, 1966, Ser. No. 570,880 Claims priority, application Switzerland, Sept. 13, 1965, 12,698/65; June 9, 1966, 8,373/66, 8,374/66 12 Claims. (Cl. 209-139) ABSTRACT OF THE DISCLQSURE A scatter type pneumatic sifter or separator includes a scattering space enclosed by an inner housing and containing a rotary scattering plate and a selector wheel. An outer housing defines a separating chamber whici surrounds the scattering space. The uppermost regions of the scattering space and the separating chamber communicate through an annular zone which contains a fan wheel. The lower regions of the separating chamber and the scattering space are formed as hoppers and are interconnected by a controlled air flow passage. A plurality of circumferentially spaced guide blades is provided and each is rotatable about an axis radial to the axis of rotation of the scattering plate. The guide blades lie beneath the selector wheel. Adjustment of the guide blades permits control of the degree of fineness of the separated material.

This invention relates to a scatter type sifter for separating coarse and fine material, more particularly for sifting cement, having a scattering space, enclosed by an inner housing and containing a scattering late and a selector wheel, arranged in a region situated axially above said scattering plate, said scattering space being surrounded by a separating chamber, which is enclosed externally by an outer housing and is connected by a lower connecting channel to the lower region of the scattering space, and also having a fan wheel, the blades whereof occupy the annular connecting zone, connecting the scattering space to the separating chamber and situated above the scattering space.

For regulating the sifting process, that is to say, the degree of fineness of the separated fine material, it is known in such scatter type sifters to vary the speed of the selector wheel for constant speed of the fan wheel. This, however, requires a hollow shaft and a core shaft, or the driving of one wheel from above and of the other wheel from below, which impairs the operating reliability, and in each case, the use of a commutator motor, unsuitable for dusty surroundings, or an expensive infinitely variable gear. In scatter type sifters, in which the selector wheel and fan wheel are driven by a constant speed three-phase motor, it is known to effect regulation of the degree of fineness by varying the number of selector blades. The mounting and removal of selector blades, however, is time-consuming and necessitates corresponding interruptions in working. In addition, neither continuous nor sufiiciently fine regulation is possible in this way.

The invention aims at overcoming these drawbacks. For this purpose, a scatter type sifter of the hereinbefore described kind is constructed according to the invention such that there is provided a ring of guide blades arranged below the ring of selector blades and rotatable about axes substantially radial to the sifter axis.

An embodiment example of the invention is represented in the drawing. The single figure shows an axial section through a scatter type sifter.

The scatter type sifter has an outer housing 1 taper- 3,395,796 Patented Aug. 6, 1968 ing downwardly in a hopper 2, and a coaxial inner housing 3, which terminates in a corresponding hopper 4 havin a connecting piece 5, leading to the outside through the wall of the hopper 2, and a rotary lock 6 mounted on its outer end. The inner housing 3 is sup ported in the outer housing 1 by means of struts 7. Mounted on a cover 8 of the outer housing 1 is a motor 9, which through a gearing 10 with shaft 11 drives a scattering plate 12. A hub 14 is connected to the scattering plate 12 by means of struts 13. The hub 14 carries a ring of selector blades 15 and a ring of fan blades 16. The scattering plate 12 and the ring of selector blades 15 are situated in the scattering space 17 located in the interior of the inner housing 3, and the ring of fan blades 16 is situated in the annular connecting zone 19 connecting the scattering space 17 with the separating chamber 18 bounded by the inner housing 3 and the outer housing 1. Substantially in the middle of the sifter, the hopper 4 of the inner housing 3 has an annular opening with guide plates 20, which opening forms a lower connecting channel 21 between the separating chamber 18 and the lower region of the scattering space 17.

When the fan blades 16 rotate, the air in the sifter makes a circuit from the connecting zone 19 to the separating chamber 18, through the connecting channel 21 to the scattering space 17 and up again in the latter to the connecting zone 19; the guide plates 20 in the connecting channel 21 catch the spinning air, and by adjustment of said plates, the circulating air current can be throttled in known manner.

The material to be sifted passes through a pipe 22 into a hopper 23 of the cover 8, and is there brought on to the rotating scattering plate 12 and projected outwardly by the latter. It then enters the current, upwardly directed at this place, of the circulating air. The coarse particles pass downwardly in known manner; if they do not fall downwardly under the action of their oWn weight, they are either retarded in their upward movement by the impact of the selector blades 15 acting on them, such that they fall downwardly, or are forced radially outward, where they impinge on the inner surface of the wall of the inner housing 3, and then fall down along the annular zone 24 between the wall of the inner housing 3 and the periphery of the ring of selector blades 15, in which zone 24 no upwardly directed air flow prevails, since over its radial region the scattering space 17 is closed by a cover ring 25, and hence the passage from the scattering space 17 to the connecting zone 19 is limited to the radial extent of the ring of selector blades 15. The fine material, on the contrary, is seized in known manner by the air current and is carried u-pwardly and passes through the connecting zone 19 into the separating chamber 18, where it is separated from the air current.

Below the ring of selector blades 15, there is arranged a ring of guide blades 26, which are secured in overhung fashion to pivots 27 with axes radial to the sifter axis, and are pivotal about their axes by means of said pivots 27. In the drawing, the guide blades 26 are shown in a position parallel to the sifter axis. Their upper edges are then directly adjacent the lower edges of the selector blades, and their lower edges extend in the sifter axis direction as far as the height of the disc 14, arranged above the scattering plate 12, of the hub 14, which disc 14' limits the extent of the scattering jet upwardly in the sifter axis direction. The disc 14 on its outer edge carries a conical guide wall 14". Its extent in the sifter axis direction corresponds to the width of the guide blades 26 in the position parallel to the sifter axis. The shape of the inner end faces of the guide blades 26 is adapted to the conical shape of the guide wall 14". Between the guide blades 26 and guide wall 14", the necessary distance is maintained for pivoting of the guide blades 26.

In the region between the guide blades 26 and the wall of the inner housing 3, the pivots 27 are surrounded by bushes 28 and are rotatably mounted therein, said bushes 28 being securely fixed in the inner housing 3. A short section of the pivots 27 projects into the separating chamber 18. Mounted on said section is a bush 29 carrying a downwardly directed link lever 30, to the bottom end of which is fixed a ball 31. The balls 31 are guided in vertical slots 32 of an adjusting ring 33, which adjusting ring is rotatably mounted on a flange 34 of the inner housing, so that by rotation of the adjusting ring by means of a device not shown, the guide blades 26 can be turned from the outside on the axes of their pivots 27.

Between the selector blades 15 and fan blades 16, there are provided slides 35 movable into the passage from the scattering space 17 to the connecting zone 19, which slides, in the position shown in the drawing, rest on the cover ring 25. These slides 35 are secured to radially extending rods 36, which are guided radially movable in openings 37 in the outer housing 1 and guides 38 on the inner housing 3. By movement of these slides 35 towards the sifter axis, the passage from the scattering space 17 to the connecting zone 19 can be blocked for the greater part. The mechanism parts 30, 31, 33 are surrounded by a hood 39. The space 40 confined by the hood 39 and by a portion of the inner housing 3 is adapted to be connected by a pipe 41 to a source, not shown, of filtered compressed air.

In sifting cement, the plant according to the invention operates as follows: In a position of the guide blades 26 viewed in the direction of flow of the circulating air in the scattering space 17, that is to say, from below upward, inclined in the direction of rotation of the selector blade wheel, a large part of the material reaching the selector wheel passes into the hopper 4. If, on the contrary, the guide blades 26 are set in such a manner that, seen in the direction of flow of the circulating air in the scattering space 17, that is to say, from below upwardly, they are inclined opposite to the direction of rotation of the selector blade wheel, a large part of the material reaching the selector wheel passes through the latter into the connecting zone 19. This phenomenon may be explained as follows. In the first case, the particles reaching the selector wheel have a direction of movement with a component corresponding to the direction of movement of the selector wheel, and therefore in particular the coarse particles will be received by the selector blades 15 without substantial shock and will be conveyed outwardly into the annular space 24. In the second case, on the contrary, the particles reaching the selector wheel have a direction of movement with a component opposite to the direction of movement of the selector wheel, so that therefore there is rebound on the selector blades 15, so that the coarse particle in particular become detached from the selector blades 15 and continue their upward path. This statement lays no claim to completeness or general applicability. Cases are conceivable in which material with other properties would give other results.

By the steps according to the invention, there is provided a sitter, in which the degree of fineness of sitting can be regulated continuously from outside by any desired degree during operation.

The guide wall 14" and the cover ring 25 ensure that the circulating stream flows within the range of the ring of selector blades 15.

It would also be possible to arrange the guide blades directly under the scattering plate and hence substantially below the scattering jet. This embodiment would have the advantage that only air practically without material would flow through the guide blades, so that the guide blades would not be exposed to any Wear.

By an additional regulation by means of the slides 35, known per se, the effect of the regulation by means of 4. the guide blades 26 is quite considerably increased. Simultaneous actuation of the two regulating devices 26, 35 is effected in a manner such that at the position of the guide blades 26 at which the quantity of material passing from the scattering space 17 to the connecting zone 19 is a minimum, the slides 35 are moved into that position near the sifter axis, in which they block to the maximum degree the passage from the scattering space 17 to the connecting zone 19. In a constructed plant for sifting cement, it was possible by means of regulation by the guide blades 26 and the slides 35 to regulate the degree of fineness of the separated fine material in a range between 0.5% and 12% residue on a sieve ASTM No. 175.

The hood 39 protects the mechanism parts 30, 31, 33 from cement dust. The introduction of filtered, compressed air into the space 40 affords additional protection against the entry of cement dust, and in the cement industry there is in any event always a suitable source of compressed air available, for example that for pneumatic conveying.

The pivots of the guide blades may also be carried radially through the separating chamber to the outside of the wall of the outer housing. In such a case, the bushes, which surround the pivots and in which the pivots are journalled, extend to the wall of the outer housing, which provides good fixing of the bushes in both housings and good mounting of the pivots in the bushes. The attachment of mechanism parts outside the outer housing 1 involves less risk of clogging such parts with dust, but even in this case, a hood is found to be more advantageous. Instead of the adjusting device shown, it is possible to use any known device for adjusting a ring of blades pivotal about axes radial to the ring axis. It is also possible to associate with each blade pivot a servomotor, which may be spring-loaded in one working direction.

What is claimed is:

1. A scatter type pneumatic sifter, comprising in combination a circular outer housing terminating downwardly in a hopper and a coaxial inner housing terminating downwardly in a hopper, said housings confining an annular separating chamber and said inner housing confining a circular scattering space; said hopper of said inner housing having openings forming a connection channel between said separating chamber and th lower region of said scattering space; an annular connecting zone being left between said inner and outer housing for connecting the uppermost region of said scattering space with said separation chamber; a rotatable ring of fan blades arranged coxially to the sifter axis in said connecting zone so as to force the air in the sifter along a closed circulatory path formed by said connecting zone, said separating chamber, said connecting channel and said scattering space; a ring of selector blades coaxial to the sifter axis rotatably arranged in the upper region of said scattering space; a scattering plate coaxial to the sifter axis rotatably arranged below said ring of selector blades; inlet duct means for passing material to be sifted to said scattering plate and outlet duct means for evacuating coarse fractions from said hopper of said inner housing and fine fractions from said hopper of said outer housing; a plurality of circumferentially spaced guide blades arranged below said ring of selector blades, said guide blades having pivots with axes radial to the sifter axis and rotatably mounted, so that said guide blades are pivotable about axes radial to the sifter axis.

2. The combination defined in claim 1, in which the upper edges of said guide blades in a position parallel to the sifter axis lie substantially within an axial region bounded by the lower edges of said selector blades and the lower edge of said scattering plate.

3. The combination defined in claim 1, in which said plurality of guide blades is arranged directly below said ring of selector blades.

4-. The combination defined in claim 3, in which said scattering plate is arranged in a region below the lower edge of said guide blades.

5. The combination defined in claim 3, in which said ring of selector blades is provided with a hub carrying said selector blades, said hub having an annular guide wall occupying the width of and being adjacent the inner edge walls of said guide blades.

6. The combination defined in claim 1, in which the length of said guide blades is substantially equal to the length of said selector blades.

7. The combination defined in claim 1, in which control means for effecting synchronous pivoting movement of said guide blades are provided, to which said pivots of said guide blades are connected.

8. The combination defined in claim 7, in which said control means comprise link levers fixed on the ends of said pivots of said guide blades remote from the latter, balls fixed on the free ends of said link levers, and an adjusting ring coaxial to the sifter axis rotatably arranged and having slots lying in planes passing substantially through the sifter axis, said balls being guided in said slots.

9. The combination defined in claim 7, in which a hood is provided which surrounds said control means.

10. The combination defined in claim 9, in which a conduit is provided which is connected to the space confined by said hood and adapted to be connected to a source of filtered compressed air.

11. The combination defined in claim 1, in which slides are provided movable into the passage from said scattering space to said connecting zone.

12. A scatter type pneumatic sifter, comprising in combination a circular outer housing terminating downwardly in a hopper and a coaxial circular inner housing terminating downwardly in a hopper, said housings confining an annular separating chamber and said inner housing confining a circular scattering space; said hopper of said inner housing having openings forming a connection channel between said separating chamber and the lower region of said scattering space; said connection channel having orientable guide blades; an annular connecting zone being left between said inner and outer housing for connecting the uppermost region of said scattering space with said separation chamber; a rotatable ring of fan blades arranged coaxially to the sifter axis in said connecting zone so as to force the air in the sifter along a closed circulatory path formed by said connecting zone, said separating zone, said connecting channel and said scattering space; a ring of selector blades coaxial to the sifter axis rotatably arranged in the uppermost region of said scattering space; a scattering plate coaxial to the sifter axis rotatably arranged below said ring of selector blades; said ring of fan blades, said ring of selector blades and said scattering plate having a common coaxial shaft; motor means for driving said shaft; inlet duct means for passing material to be sifted to said scattering plate and outlet duct means for evacuating coarse fractions from said hopper of said inner housing and fine fractions from said hopper of said outer housing; a pinrality of circumferentially spaced guide blades arranged between said ring of selector blades and said scattering plate, said guide blades having pivots with axes radial to the sifter axis and rotatably mounted, so that said guide blades are pivotable about axes radial to the sifter axis; the upper edges of said guide blades in a position parallel to the sifter axis lying directly below said selector blades and the lower edges of said guide blades lying in an axial region above said scattering plate; the length of said guide blades being substantially equal to the length of said selector blades; a hub carrying said selector blades having an annular guide wall occupying the width of and being adjacent the inner edge walls of said guide blades; control means for effecting synchronous pivoting move -ment of said guide blades, arranged in said separating chamber, comprising link levers fixed on the ends of said pivots of said guide blades remote from the latter, balls fixed on the free ends of said link levers, and an adjusting ring co-axial to the sifter axis rotatably arranged, and having slots lying in planes passing through the sifter axis, said balls being guided in said slots; a hood surrounding said control means; a conduit connected to the space confined by said hood and adapted to be connected to a source of filtered compressed air; and slides movable into the passage from said scattering space to said connecting zone.

References Cited UNITED STATES PATENTS 2,206,981 7/ 1940 Sturtevant 209139 FOREIGN PATENTS 805,840 5/1951 Germany.

FRANK W. LUTTER, Primary Examiner. 

